Old speakers: bass causing abnormal vibration

2013-04-07 14:16:34

I have an old system of stereo speakers of mostly a nostalgic value (my dad had them when I was a kid) that started showing the following behavior: on heavy bass, one of the speakers produces clanging noises as if the speaker is hitting something from the vibration.

It only really affects one of the speakers and only on really heavy bass. I don't know anything about speaker's internal workings but could it be that some kind of mount loosened over time and is not holding the speaker in place? Or is it just "normal" wear and tear and there is nothing to be done?

Old speakers: bass causing abnormal vibration

Yes, it's not a scratching noise, sounds pretty much metallic. I didn't try to open the box yet, not even sure it's possible without having to break it apart. From the front, only the normal movement of the membrane is visible.

Old speakers: bass causing abnormal vibration

Yes, it's not a scratching noise, sounds pretty much metallic. I didn't try to open the box yet, not even sure it's possible without having to break it apart. From the front, only the normal movement of the membrane is visible.

How is the speaker element itself attached? Taking it out might be the easiest way to inspects the innards of the box.

Old speakers: bass causing abnormal vibration

I just took the bigger one out (man are they heavy), they are fixed to the front plane with four screws. There are no apparent cracks or anything on the supporting mount. About the only thing that is suspicious is that one of the 4 screws cannot be tightened, probably the winding is giving out.

It doesn't seem to be related to the noise I'm hearing. I removed the whole (metal!) backplate including the integrated amp and the noise mostly stopped. Now all I hear is slight crackling from the tweeter my younger brother poked in. I think the sound was coming from the backplate. The insulation(?) between it and the backplate has long disintegrated, so maybe even tightening the screws doesn't help.

Just making sure, as long as the speakers are in passive mode, the capacitors etc are "safe" to touch, right? I'd want to dismount the tweeter and try to pop the membrane back into spherical form. Would that be a bad idea?

Old speakers: bass causing abnormal vibration

Tricky - I would try to do it from the front, using a small needle to grab the dome.

Hmm, without piercing it, though? I'm not sure how this one works but I can't imagine it would like a hole pierced into it to grab the dome.I thought it would be possible to push the dome from the inside, but the thing looks solid...

Old speakers: bass causing abnormal vibration

Hmm, it seems to be something different than the transformer mounting. I reassembled the whole thing and the sound is back. It does go away once i remove the whole backplate. I don't know if pictures would help you, but I can take some if you tell me what you want to see...

The dome didn't want to bend back completely, but the crackling is now much less than before.

edit: ok, so I took the backplate from the working speaker, and put it into the defective one - the same thing happens. Now it's not a metallic sound anymore though, it sounds like two pieces of rubber or plastic rubbing on each other. As if putting the backplate on causes the bass to become too strong and it's pushing the membrane in recoil... or something

Old speakers: bass causing abnormal vibration

I have an old system of stereo speakers of mostly a nostalgic value (my dad had them when I was a kid) that started showing the following behavior: on heavy bass, one of the speakers produces clanging noises as if the speaker is hitting something from the vibration.

It only really affects one of the speakers and only on really heavy bass. I don't know anything about speaker's internal workings but could it be that some kind of mount loosened over time and is not holding the speaker in place? Or is it just "normal" wear and tear and there is nothing to be done?

Look inside the box. Something might be loose. If it is, tighten it up.

You acess the inside of most loudspeaker systems by removing the largest driver with a few screws.

Old speakers: bass causing abnormal vibration

edit: ok, so I took the backplate from the working speaker, and put it into the defective one - the same thing happens. Now it's not a metallic sound anymore though, it sounds like two pieces of rubber or plastic rubbing on each other. As if putting the backplate on causes the bass to become too strong and it's pushing the membrane in recoil... or something

If you move the woofer in & out (carefully) by hand, do you hear/feel any rubbing? Sometimes a woofer can sag out of alignment and you can get rubbing of the voice coil (or voice coil form) in the magnet gap.

Sometimes you can minimize that by rotating the woofer. (As a test, you can turn the whole speaker upside-down.)

Sometimes the voice coil can start to come loose and rattle (metallic sound).

Speakers can be reconed. (The speaker cone, voice coil, and suspension are replaced. The magnet & basket are re-used.)

Or you can replace the woofer, which is often cheaper. The problem with replacing the woofer is that the original woofer was (hopefully) matched to the cabinet design, the crossover, and the tweeter. If you can't get an exact factory replacement, the speaker characteristics will change, and if you don't replace the pair, the left & right won't sound alike.

Reconing should give you a speaker closer to the original, but I'd probalby recone both of them to keep them both the same.

Old speakers: bass causing abnormal vibration

I have an old system of stereo speakers of mostly a nostalgic value (my dad had them when I was a kid) that started showing the following behavior: on heavy bass, one of the speakers produces clanging noises as if the speaker is hitting something from the vibration.

It only really affects one of the speakers and only on really heavy bass. I don't know anything about speaker's internal workings but could it be that some kind of mount loosened over time and is not holding the speaker in place? Or is it just "normal" wear and tear and there is nothing to be done?

I bought my speakers some time ago second hand. First one and then a month later the other bass speaker developed what I called at the time a 'death rattle' only with deep bass notes, which was distinctly metal on metal, very much as you have described . I assumed that they had been thrashed, it was more cost effective for the dealer to fit a new speaker than to have it repaired.

Old speakers: bass causing abnormal vibration

If you move the woofer in & out (carefully) by hand, do you hear/feel any rubbing? Sometimes a woofer can sag out of alignment and you can get rubbing of the voice coil (or voice coil form) in the magnet gap.

That was why my first question was about the sound - metallic rattle vs. scratching. Cured a couple of KEF139's by turning them upside down.

I think you can hear it best at the start of the sample, the ... *skrskrskr*-like post-bass oscillation (?). I don't really get why the noise only comes back with the speaker box completely assembled...

I don't think replacing a driver of a soviet era speaker with an identical model would be possible Reconning sounds like an idea, if it's really the cone that shifted. But then I'd hear a pure metallic sound, right?

Moving it by hand doesn't reveal any rubbing. I will try soldering it over to the other box to be completely sure it's the speaker itself.

Old speakers: bass causing abnormal vibration

That doesn't seem to be it. It seems to be air escaping between the backplate and the casing, at least when I loosen the screws the sound is louder and I can feel air escaping through the slits. It doesn't really explain why the other speaker doesn't have this behavior, unless they're actually not the same on the left and the right... and the one on the "left" (aka "bad") simply has more oomph.

I now soldered it unto the right box and the sound is still the same, so it seems somehow related to this one driver after all. I will try putting new insulation between the backplate and the case, and see if it changes anything.

Old speakers: bass causing abnormal vibration

Well, I'd say it's a partial success. The annoying sound is now much lower and only starts appearing on volumes I don't feel comfortable listening to. I guess the rest of it comes from the one speaker being more worn out than the other one =/

They're still usable at normal volumes with the majority of the tracks, and that's enough for me. Thank you for all the help.

Old speakers: bass causing abnormal vibration

Yes, I did both, no change. So it's probably a defective driver. I doubt it's worth replacing it though, I know too little about driver characteristics in general and finding out the exact specs is a bit hard. I actually found out the company who made these still exists and they're listing this driver as "EOL, no modern analogues exist". Specs are also not listed.

Edit: these are the speakers btw: clickThey mention the 3 drivers for the high/middle/low frequencies and two passive filters, 700Hz and 5000Hz

Old speakers: bass causing abnormal vibration

...I doubt it's worth replacing it though, I know too little about driver characteristics in general and finding out the exact specs is a bit hard.

Of course that's up to you... If it was me I'd probably replace them with something. Those are cool-unique looking speakers, and with the nastalgic value it would be worth it to me. I assume you are not in the U.S., but just for example, Parts Express has 8-inch woofers starting at $11 USD. (It looks like about 8-inches.) If you replace the woofer with a new "cheap" woofer and it sounds worse, you can always put the old one back in.

You can usually get the Thiele-Small parameters for any new woofer, and with WinISD (FREE!!!) you can predict bass performance in your existing cabinets, if you wish to make the effort.

Old speakers: bass causing abnormal vibration

The driver is 25cm in diameter (24,5cm if not counting the mounting itself), which is 9.8 inches according to google. I think the problem would be the peculiar form of the mount. You can see it if you search this page for "75ГДН-5", though mine actually look exactly like the "75ГДН-1-4" (despite being labeled 75ГДН-5)

I'd probably have to modify the cabinet to fit a new driver somehow. From my understanding a "closed box" design has to be more or less airtight to not suffer from "wheezing"? I might need some kind of a guide to different cabinet types and what is required :x

I'm sure there are some German members around here, so maybe someone could point me to a good place to get the drivers? I tried looking at amazon.de, but the biggest they have is 20cm. The funny thing though, the one I found has the same peculiar form mine have ^^

edit: uhm. I think I just found a more recent version of the radiotehnika site. Whichever the official one is lol. Anyway, the other site has the full specs in English (though the site is still latvian/russian only): click